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<H2>advance()</H2>
<P><B>Module:</B>&nbsp;&nbsp;Standard C++ Library&nbsp;&nbsp;&nbsp;<B>Library:</B>&nbsp;&nbsp;<A HREF="2-8.html">Iterators</A></P>

<PRE><HR><B><I>Function</I></B><HR></PRE>

<UL>
<LI><A HREF="#sec1">Local Index</A></LI>
<LI><A HREF="#sec2">Summary</A></LI>
<LI><A HREF="#sec3">Synopsis</A></LI>
<LI><A HREF="#sec4">Description</A></LI>
<LI><A HREF="#sec5">Example</A></LI>
<LI><A HREF="#sec6">See Also</A></LI>
<LI><A HREF="#sec7">Standards Conformance</A></LI>
</UL>
<A NAME="sec1"><H3>Local Index</H3></A>
No Entries
<A NAME="sec2"><H3>Summary</H3></A>
<P>A function that advances an iterator forward or backward (if available) by a certain distance</P>
<A NAME="sec3"><H3>Synopsis</H3></A>

<PRE>#include &lt;iterator&gt;

namespace std {
  template &lt;class InputIterator, class Distance&gt;
  void advance(InputIterator&amp; i, Distance n);
}
</PRE>
<A NAME="sec4"><H3>Description</H3></A>
<P>The <SAMP>advance()</SAMP> function template allows an iterator to be advanced through a container by some arbitrary distance. For bidirectional and random access iterators, this distance may be negative. For random access iterators, this function uses <SAMP>operator+=()</SAMP> and <SAMP>operator-=()</SAMP> for constant time implementations. For input, forward, and bidirectional iterators, <SAMP>advance()</SAMP> uses <SAMP>operator++()</SAMP> for linear time implementations. <SAMP>advance()</SAMP> also uses <SAMP>operator--()</SAMP> with bidirectional iterators for linear time implementations of negative distances. </P>
<P>If <SAMP>n</SAMP> is positive, <SAMP>advance()</SAMP> increments iterator reference <SAMP>i</SAMP> by <SAMP>n</SAMP>. For&nbsp;negative&nbsp;<SAMP>n</SAMP>, <SAMP>advance()</SAMP> decrements reference <SAMP>i</SAMP>. Remember that <SAMP>advance()</SAMP> accepts a negative argument <SAMP>n</SAMP> for random access and bidirectional iterators only.</P>
<A NAME="sec5"><H3>Example</H3></A>

<UL><PRE>//
// advance.cpp
//

#include &lt;iterator&gt;   // for advance
#include &lt;iostream&gt;   // for cout, endl
#include &lt;list&gt;       // for list



int main ()
{
    // Typedefs for convenience.
    typedef std::list&lt;long, std::allocator&lt;long&gt; &gt; list;
    typedef std::ostream_iterator&lt;list::value_type, char,
                              std::char_traits&lt;char&gt; &gt; os_iter;

    // Initialize a list using an array.
    const list::value_type arr [] = { 3, 4, 5, 6, 7, 8 };
    list l (arr + 0, arr + sizeof arr / sizeof *arr);

    // Declare a list iterator, s.b. a ForwardIterator.
    list::iterator itr = l.begin ();

    // Output the original list.
    std::cout &lt;&lt; "For the list: ";
    std::copy (l.begin (), l.end (), os_iter (std::cout, " "));

    std::cout &lt;&lt; std::endl &lt;&lt; std::endl
          &lt;&lt; "When the iterator is initialized to l.begin ()," 
          &lt;&lt; "\nit points to " &lt;&lt; *itr &lt;&lt; std::endl;

    // operator+ is not available for a ForwardIterator, 
    // so use advance.
    std::advance (itr, 4);
    std::cout 
      &lt;&lt; "\nAfter advance (itr, 4), the iterator points to "
      &lt;&lt; *itr &lt;&lt; std::endl;

    return 0;
}

Program Output:
For the list: 3 4 5 6 7 8 

When the iterator is initialized to l.begin (),
it points to 3

After advance (itr, 4), the iterator points to 7
</PRE></UL>
<A NAME="sec6"><H3>See Also</H3></A>
<P><A HREF="sequences.html">Sequences</A>, <A HREF="randomaccessiterators.html">Random Access Iterators</A>, <SAMP><A HREF="distance.html">distance()</A></SAMP></P>
<A NAME="sec7"><H3>Standards Conformance</H3></A>
<P><I>ISO/IEC 14882:1998 -- International Standard for Information Systems -- Programming Language C++, Section 24.3.4</I></P>

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